Incinerator with extended heat exchange surface

ABSTRACT

An incinerator for a drying oven and the like to remove combustible fumes such as solvent vapors from the exhaust from such ovens. The incinerator is formed from a narrow, elongated, heat conducting, metal incinerator conduit having at least one U or reverse bend to increase turbulance within the conduit and to increase heat exchange of hot gases with the exterior of the conduit. The incinerator conduit is formed of a plurality of elongated arcuate sections which are secured together at the edges. Heat conducting fins extend through the conduit between the interior and the exterior thereof at the edges of the arcuate sections to facilitate heat transfer between the interior and exterior of the incinerator conduit. The fume-laden gases to be incinerated are channelled along the exterior surface of the incinerator conduit in contact with the heat exchange fins by a larger preheat conduit surrounding the incinerator conduit. A fan draws the solvent-laden gases through the larger preheat conduit and forces the preheated gases into the incinerator conduit at a higher pressure than that of the preheat conduit.

United States Patent Phillips [15] 3,670,668 1 June 20, 1972 INCINERATORWITH EXTENDED HEAT EXCHANGE SURFACE [72] Inventor: William A. Phillips,Comstock Park, Mich.

[73] Assignee: Granco Equipment, Inc., Grand Rapids,

Mich.

' 22 Filed: Jan. 8, 1971 [21] App1.No.: 104,912

[52] U.S.C1... ....ll0/8 A,23/277C [51] Int. Cl. ..F23g 7/00 [58] FieldoiSearch ..1 10/8, 8 A; 23/277C [56] References Cited 7 UNITED STATESPATENTS 3,189,416 6/1965 Clarke et a1. "23/277 3,472,498 10/1969 Priceet al .23/277 X 3,484,189 12/1969 Hardison et al ..23/277 X 3.549.33312/1970 Tabak ..1l0/8 X Primary Examiner-Kenneth W Sprague Attorney-JohnE. McGarry ABSTRACT An incinerator for a drying oven and the like toremove combustible fumes such as solvent vapors from the exhaust fromsuch ovens. The incinerator is formed from a narrow, elongated, heatconducting, metal incinerator conduit having at least one U or reversebend to increase turbulance within the conduit and to increase heatexchange of hot gases with the exterior of the conduit. The incineratorconduit is formed of a plurality of elongated arcuate sections which aresecured together at the edges. Heat conducting fins extend through theconduit between the interior and the exterior thereof at the edges ofthe arcuate sections to facilitate heat transfer between the interiorand exterior of the: incinerator conduit. The fume-laden gases to beincinerated are channelled along the exterior surface of the incineratorconduit in contact with the heat exchange fins by a larger preheatconduit surrounding the incinerator conduit. A fan draws thesolvent-laden gases through the larger preheat conduit and forces thepreheated gases into the incinerator conduit at a higher pressure thanthat of the preheat conduit.

17 Claims, 4 Drawing Figures P'A'TENT'EUJum m2 SHEET 2 BF 2 FIG.2

INVENTOR.

WILLIAM A. PHILLIPS FIG. 3

ms ATToQN sy INCINERATOR WITH EXTENDED HEAT EXCHANGE SURFACE BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates toincineration of combustible fumes. In one of its aspects, the inventionrelates to a fume incinerator having an improved heat exchanger forrecovery of heat of oxidation of the fumes for preheat of thefume-containing gases prior to incineration.

2. State of the Prior Art In copending, US. patent application, Ser. No.59,142, filed July 29, 1970, assigned to the same assignee of thispatent application, there is disclosed and claimed a solvent di'yingoven with an integrated incinerator formed of an elongated metal burnertube, said tube having at least one U-bend. Solventladen gases areremoved from the oven, heat exchanged with the burner tube, drawnthrough a fan and then forced into the interior of the burner tubewherein the solvent and other combustible material in the gases isincinerated. In one embodiment, the solvent-containing gases are drawnthrough the annulus of a second larger tube which encircles the burnertube.

In the incineration of such gases, it is necessary to raise thetemperature of the solvent and air mixture from the oven temperature tothe incineration temperature. For drying ovens for lithographed sheets,for example, the temperature of the oven gases must be raised from about400 F to about l,300 F. Such a temperature rise requires a considerableamount of fuel which adds substantially to the expense of the dryingoperation. Not only is the fuel expensive but it is currently in shortsupply. However, the oxidation of the solvent is an exothermic reactionwhich yields a significant amount of heat which can be recovered toconverse energy requirements of the incineration process. For recoveryof such heat, the incinerator tube should have a maximum surface areawhich can contact the hot gases.

Solvent drying ovens are subject to shut down for short periods of timeas well as for extended periods of time. Fuel could be conserved if thesolvent incinerator could be shut down while the dryingoven is shut downor idling. However, conventional refractory lined incinerators depend onthe heat of the refractory to maintain the incineration temperatures andtherefore have a relatively long lag time which requires suchincinerators to be run almost continuously. When the drying oven is shutdown for long periods of time, the refractory incinerators can be shutdown, but it takes considerable time and fuel to bring the refractoryincinerators up to temperature when the ovens are started again. Forthese reasons, refractory lined incinerators are expensive to operate.

On the other hand, metal incinerators have a very fast recovery time.Heretofore, these metal incinerators have of necessity been of weldedair-tight construction to avoid leaks of combustible material into theatmosphere. Such construction requires heavy gauge high temperaturemetals which are themselves expensive and are expensive to fabricate.The temperature cycling of the incinerator results in fatigue of thewelded joints of the metal incinerator. Once the welded joints developcracks or holes, the costly incinerator becomes ineffective and must bescrapped. Further, some metal incinerators have been of a large diameterwith a minimum of surface area with which heat exchange can beaccomplished. In addition, the heavy gauge metal used in theseincinerators militates I OBJECTS By various aspects of this inventionone or more of the following, or other, objects can be obtained.

It is an object of this invention to provide an efficient and effectiveincinerator for use in oxidizing solvents and the like, the incineratorhaving a fast response time which can be operated responsive to overoperating conditions so that it can be shut down when the oven is notoperating, thereby minimizing the cost of incinerating the solvents, yetof such a construction as to avoid metal fatigue of welded joints due totemperature cycling.

It is another object of this invention to provide a compact and small,but highly efficient, incinerator for fume-laden gases and the likewhich incinerator can be incorporated into drying ovens, or mountedadjacent existing ovens, for incineration of fumes developed duringdrying and baking processes within the ovens.

It is another object of this invention to provide a highly efficient anddurable incinerator for solvent gases and the like which is inexpensiveto manufacture and highly reliable in operation.

It is another object of this invention to provide an incinerator forsolvent gases and the like wherein effective heat exchange is carriedout directly with the incinerator itself.

It is another object of this invention to provide an incinerator forsolvent-laden gases and the like, the incinerator having an inexpensive,yet highly effective, heat exchanger to reduce the cost of incineratingthe fumes.

It is yet another object of this invention to provide a high temperaturemetal incinerator having a surrounding heat exchanger which operateseffectively enough to keep the outer surface of the incinerator unitrelatively cool to permit mounting of the unit within a building, withinan oven or closely adjacent thereto with a minimum of insulation and toextend the life of the metallic reactor.

It is another object of this invention to providea high temperaturemetal incinerator of flexible construction which minimizes the effect oftemperature cycling on the incinerator.

It is another object of this invention to provide a metal incinerator ofinexpensive construction which eliminates the adverse effects of leaksin the reactor body.

It is another object of this invention to provide a metal tubularincinerator for high velocity incineration of gases containing solventsand other combustible materials.

Another object of this invention is to provide a heat exchanger with anextended surface for maximum heat transfer between the interior andexterior of the incinerator tube.

Other aspects, objects, and the several advantages of this invention areapparent to one skilled in. the art from a study of this disclosure, thedrawings, and the appended claims.

BRIEF STATEMENT OF THE INVENTION According to the invention, anincinerator for solvent-laden gases has a narrow elongated burner tubesurrounded by a heat exchange housing for preheating the gases. Heatexchange fins extend from the heat exchanger area outside the burnertube through the walls of the burner tube and into the interior of theburner tube to greatly enhance heat transfer between the burner tube andthe gases. A fan draws the solvent-laden gases over the outer surface ofthe burner tube and in contact with the heat exchange fins, and thenforces the heat exchanged gases through the burner tube at a higherpressure wherein they are further heated and incinerated. The fancreates a higher pressure within the burner tube than outside the tubeso that any leaks from the burner tube escape into the preheating gasesand are recycled through the incinerator.

The burner is advantageously made from elongated panels which aremechanically fastened together with heat exchange fins extendingtherebetween. For such purposes, the panels can be provided withoutwardly extending flanges through which the mechanical fastenersextend. Preferably, the burner tube has at least one U or reverse bendto minimize the space requirements and to turbulate the gases within thetubes, thereby increasing mixing and incineration of the solvents andincreasing the heat exchange properties of the gas. The burner tubeconstruction need not be of air tight welded construction. Preferably,the construction of the burner tube is such that a small fraction of thehot gases escape from the burner tube into the preheat area. Escapementof hot gases through the walls of the burner tube provide direct heatexchange between the oxidized gases and the solvent-air mixture, andthereby enhances the heat exchange quality of the incinerator.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be describedwith reference to the accompanying drawings in which:

FIG. 1 is a perspective view, partially broken away, illustrating anincinerator unit according to the invention;

FIG. 2 is a partial side elevational view, in section, of theincinerator unit illustrated in FIG. 1;

FIG. 3 is a partial sectional view taken along lines llI-Ill of FIG. 2;and

FIG. 4 is a perspective view of component parts of theincinerator tube.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to thedrawings, there is illustrated an incinerator unit generally designatedby the numeral 14 mounted on top of solvent drying oven generallydesignated by the numeral 12. The incinerator 14 is formed from an outerhousing 16 of insulating material and has openings 18, 20 and 22 in thebottom thereof communicating with the upper portion of the drying oven12. A dividing wall 24 extends between the bottom, top and side walls ofthe housing 16, thereby dividing the incinerator into an intake sectionor zone 25 and an incinerator and heat exchange section or zone 27. Avertical wall 26 within the intake section or zone 25 extends upwardlyfrom a floor of the housing 16 and joins a horizontal wall 28 to definea fan intake section or zone 25a within the intake section or zone 25.The vertical wall 26 and horizontal wall 28 extend between the sides-ofthe housing 16 thereby completely closing off and sealing the intakesection 25 from the fan intake section 25a. A U-shaped outer tube 30 ismounted within the incineration and heat exchange section. This tube 30has an upper open end communicating with a hole 31 in the dividing wall24. The lower open end of the U- shaped outer tube 30 communicates witha hole 33 in a bottom portion of the wall 24. Thus, the U-shaped outertube 30 communicates at one end with the intake section or zone 25 andat the other end with the fan intake section 25a.

Mounted within the U-shaped outer tube 30 is a U-shaped incinerator tubeformed of a first burner tube section 40, a U- bend section 44, and astraight upper section 46. The annular area within the U-shaped outertube 30 approximates the area within the burner tube formed by sections40, 44, and 46. Gases from this incinerator tube are exhausted fromsection 46 through an elbow section 48 and an exhaust conduit 50. Theincinerator tube section communicates with a cylindrical burner housing38 which contains a suitable fuel burner 39. Means (not shown) areprovided for supplying fuel to the burner 39. A suitable burner is aZephyr gas burner manufactured by the North American ManufacturingCompany, 4455 E. 71st Street, Cleveland, Ohio, 44l05. The burner has aspark plug (not shown) or other suitable means to initiate combustion ofthe fuel.

A fan 32 having an inlet 34 and an outlet 36 is mounted within the fanintake section 25a. The fan inlet 34 communicates with the lower portionof the outer tube 30 through the fan intake section 25a and hole 33. Theblower or fan outlet 36 communicates with the cylindrical burner housing28 and the burner 39.

The lower incinerator tube section 40 and the upper straight section 46are formed from elongated metal burner tube panels 60, best illustratedin FIGS. 3 and 4. Each elongated panel 60 is formed from an elongatedarcuate portion 62 with backwardly bent flanges 64 and 66. Holes 68 areprovided in spaced relationship along flanges 64 and 66.

Heat exchange fins 70 extend between the interior of the incineratortube sections 40 and 46 and the annular preheat area between theincinerator tube and the outer U-shaped tube 30. Such fins are of highheat conducting metal and comprise a central portion 72 having spacedtherealong a plurality of holes 74, an outer fin 76 and an inner fin 78.As illustrated in FIG. 3, bolts 80 extend through the holes 68 in theflanges 64 and 66 and through the holes 74 of the heat exchange fins tosecure the heat exchange fins in place and to secure the burner panelstogether. Thus, the burner panels are bolted together with the heatexchange fins extending therebetween. The outer heat exchange fins 76then act as spacers between the burner tube and the U-shaped outer tube30. For purposes of simplicity, these fins 76 have not been shown inFIG. 1.

The inner fins 68 extend into the incinerator tube as far as possible tomaximize heat transfer to the annular preheat area. Desirably the fins68 extend one-third to one-half of the radial distance between theburner panels 60 to the center of the incinerator tube.

In operation, solvent and air mixture at about 300 F to 400 F is drawnfrom the drying or baking oven 12 through opening 20 into the intakesection or zone 25 of the incinerator. These solvent-laden gases passthrough the annular space between the U-shaped outer tube 30 and theincinerator burner tube formed by the straight section 46, the U-bendsection 44 and the incinerator tube section 40. While passing throughthe annular space, these gases will contact the hot surface of thesetubes and will also contact the outer fins 76 of the heat exchange fins70. The contact between the gases and these hot surfaces preheat thegases as they pass through the annular space, the temperature reachingabout 800 F by the time the gases reach the fan 32. The U-bend in thetube 30 has a turbulating effect on the gases passing through theannular space which further increases the transfer of heat from the hotsurfaces to the gases.

The preheated gases are then drawn in through intake 34 of fan 32 andpassed at a higher pressure through the fan outlet 36 through burner 39and into the incinerator tube section 40. The fan 32 serves to draw thefume-laden gases through the annular preheat area within the U-shapedouter tube 30 and to increase the pressure of the preheated gases whichflow into the incinerator tube section 40. Thus, the gas pressure withinthe incinerator tube (section 40, U-bend 44, and straight section 46)will be greater than the pressure in the annular preheat area betweenthe U-shaped outer tube 30 and the incinerator tube. The above describedconstruction of the tube sections 40 and 46 show inexpensiveconstructions which need not be airtight. Since the pressure is higherin the incinerator tube section 40 than in the annular preheat area, asmall percentage of the hot gases within the incinerator tube can escapethrough the walls of the incinerator tube sections 40 and 46 into theannular preheat area. These gases will be recycled back into theincinerator tube through the fan 34. The effect of these hot gasespassing from the interior of the incinerator tube into the preheat areais to assist in the preheating of the gases by direct transfer of theheated gases. Because of the higher pressure within the burner tube andoutside the outer tube 30, the incombusted solvent gases in the preheatarea cannot bypass the incinerator section and pass into the atmosphere.The stringent governmental requirements of pollution control devicesmake it necessary that all gases go through the entire incinerator inorder to reduce the polluting gases to acceptable standards.

Gas is supplied from a source (not shown) to the burner 39 to furtherheat the gases passing therethrough to about l,200 F to l,400 F. At thistemperature, the solvents and other combustible material will besubstantially completely oxidized to carbon dioxide. The heat of thesegases is transferred through the walls of the incinerator tube (sections40, 44, and 46) to the preheat area. In addition, the hot gases withinthe incinerator tube contact the inner fins 78 of the heat exchange fins70 which transfer the heat by conduction to the outer fins 76. Becausethe elongated burner tube panels 60 are not required to be weldedtogether to form an air tight tube, lighter gauge materials can be usedfor these elongated portions 62. These lighter materials facilitatestill further the rapid heat transfer between the interior and exteriorof the burner sections 40 and 46.

The U or reverse bend formed by U-bend section 44 serves to turbulatethe gases flowing through the interior of the burner tube. Thisturbulation increases the mixing of the gases within the tube toincrease the oxidation of the combustible materials within the mixture,thereby substantially completely combusting the oxidizable materials.The turbulation produced by the U-bend section 44 further enhances theheat transfer properties of the gases so that more heat is transferredbetween the interior and exterior of the burner tube sections. Othertypes of turbulators, such as within the tubes, can be employed in theevent that a straight tube is desired.

The flow of the gases through the burner tube is quite rapid. Forexample, it has been found that the gases can pass through the tube atrates as high as 5,000 to 6,000 feet per minute. It has been found thatfor velocities of about 5,000 feet per minute and an incinerator pathlength of 25 feet with a U- bend, the residence time of the gases isapproximately 0.3 second. Even with this extremely low residence time,it has been found that 812 pounds of carbon in the form of methylethylkeystone solvent passing through the incinerator tube during an 8-hourday can be reduced to 1.3 pounds of carbon in uncombusted form. Theremainder of the carbon is substantially converted to carbon dioxide.

The incinerator tube is constructed in a narrow elongated form asillustrated in the drawings. The elongated form maximizes the surfacearea of the tube for preheating the gases to conserve fuel costs ofincineration. The length of the tube depends on the degree of preheatingrequired for the solventladen gases. It has been found that a tubelength of about 25 feet formed by two tubes 12 to 16 inches in diameterand feet long with a U-bend section therebetween, are suitable forincineration of the solvent to values within the most stringentgovernmental limits and for preheating the solvent-laden gases.

The incinerator device illustrated can also be used for maintaining heatin an oven. The oven gases pass through opening 18 in the bottom ofhousing 16 and contact the outer surface of the U-shaped outer tube 30.This contact serves to heat these gases which are then recirculated tothe furnace through fan 54. The heated gases are drawn in through theintake 56 of fan 54 and are forced through the outlet 58 back into theoven 12. Additional heat can be supplied to these gases by the trimburner 52.

Whereas the invention has been described with reference to a singleincinerator tube, it is within the scope of the invention to use aplurality of such incinerator tubes in juxtaposed relationship forlarger furnaces. The number of tubes will depend on the capacity of thefurnace.

The incinerator device described is of metal construction and has a veryrapid response time. In other words, the operation of the incineratortube can be correlated with the oven or ovens with which it works. Whenthe oven is down for short or extended periods of time, the incineratortube can be shut down. When the oven starts up, the incinerator tubewill reach its incinerating temperature in a matter of seconds. In thismanner, the amount of fuel required to operate the incinerator isfurther reduced.

The unit described is a small compact unit which can be integrated withan existing oven. It can be mounted on top of the oven or immediatelyadjacent thereto. The U-bend, in addition to the turbulating function,also makes the unit compact. This kind of unit saves valuable plantspace and avoids the heat loss and expense of ducting from an oven toexterior locations which are often required for other types ofincineration units. The high velocity of the gases through the smallunit and the turbulation effected in this unit eliminates the need forlarger incinerator reactors. Because the unit is small and can bemounted on top or immediately adjacent an existing oven, it permitsfurther heat recovery by using the heat of oxidation for heating of theoven gases. As illustrated in the drawings, the oven gases can becirculated around the U-shaped outer tube to provide heating of the ovengases.

The incinerator is of inexpensive and flexible construction. Thin gaugematerial is less expensive and welding is minimized. Leakage of hotgases from the main burner tube favorably affect the economy of theincineration process, and do not adversely affect the incineratingqualities of the device. Further, the flexible construction avoids metalfatigue due to the temperature cycling which is required of such anincinerator for optimum economical operation. The novel heat exchangerconstruction effectively preheats the gases thereby further cutting thefuel costs for operation of the incinerator unit. The heat exchangeconstruction is quite inexpensive as compared with other welded and leakproof structures. The heat exchange quality of this device also coolsthe U-shaped outer tube 30 as well as the inner burner tube to extendthe life of these metal parts. In addition, the hotter burner tube isinsulated by the preheating gases, thus permitting installation of thisincinerator within or immediately adjacent to a drying oven without thenecessity of providing expensive and bulky insulating material.

The elongated panels 60 illustrated in the drawings have been shown ashaving an arcuate configuration in crosssection. The panels 60 can bemade in many different cross-sectional shapes. For example, the panelscan have a straight cross-section so that the resulting tubularcross-section represents a regular polygon rather than a circle.Further, the panels can be corrugated for still more heat transfersurface area.

The preferred embodiment of the invention has an annular preheat areasurrounding the elongated burner tube. However, the heat exchange meansbetween the'burner tube and the preheat area can take various otherforms. For example, the preheat area can be formed entirely within theburner tube so that the burner tube becomes an annular space around apreheat conduit. In addition, a second preheat conduit can be formedaround the outside of the burner tube with the result that the annularburner tube will have preheat areas along its outer and inner surfaces.

Reasonable variation and modification are possible within the scope ofthe foregoing disclosure, the drawings, and appended claims withoutdeparting from the spirit ofthe invention.

The embodiments of the invention in which an exclusive property orprivilege are claimed are defined as follows:

1. In an incinerator for oxidizing combustible fumes contained in amixture of such fumes and air, said incinerator comprising:

a narrow elongated burner tube having an inlet end and an outlet end; i

means in said elongated tube for heating gases passing therethrough toan elevated temperature suitable for oxidizing said combustible fumes insaid mixture;

means surrounding at least a portion of said elongated burner tubedefining a preheat zone for said mixture, said surrounding meansincluding an inlet opening for receiving said mixture and an outletopening for discharging said mixture;

means for passing preheated gases from said outlet opening of saidsurrounding means into said burner tube;

the improvement which comprises:

heat exchange means extending from within said burner tube, through saidburner tube and into said preheat zone, whereby heat is effectivelytransferred from said burner tube to said preheat zone to preheat saidmixture passing therethrough.

2. An incinerator according to claim 1 wherein said burner tube containsat least one turbulating means.

3. An incinerator according to claim 1 wherein said burner tubecomprises a plurality of elongated panels joined together at thelongitudinal edges thereof, and said heat exchange means are positionedbetween said longitudinal edges of said elongated panels.

4. An incinerator according to claim 3 wherein backwardly bent flangesare formed on said longitudinal edges of said elongated panels, andfurther comprising fastening means securing together flanges of adjacentpanels with said heat exchange means therebetween.

5. An incinerator according to claim 4 wherein said fastening meansextend through said flanges and through said heat exchange means, andsaid fastening means are spaced along the length of said elongatedpanels, and said passing means includes a fan to draw said mixturethrough said preheat zone and to force the same into said burner tube ata higher pressure than that of said preheat zone.

6. An incinerator according to claim 4 wherein said heat exchange meanscomprise elongated thin metal plates which extend into said burner tubeone-third to one-half of the radial distance between the circumferenceof said burner tube and the center thereof.

7. An incinerator according to claim 4 wherein said heat exchange meanscomprise elongated thin metal plates, there being a plurality of suchelongated metal plates between each of said elongated panels, and theouter and inner longitudinal edges of said plates are bent away fromeach other.

8. An incinerator according to claim 1 wherein said heat exchange meansextend outwardly to said surrounding means and form spacers between saidburner tube and said surrounding means.

9. An incinerator according to claim 1 wherein said surrounding means isa tubular member in concentric relationship to said burner tube.

10. An incinerator according to claim 9 wherein said inlet opening ofsaid surrounding means is adjacent to said outlet end of said burnertube, and said outlet opening of said surrounding means is adjacent tosaid inlet end of said burner tube, whereby the flow of said mixturethrough said preheat zone is countercurrent to the flow of gases throughsaid burner tube.

11. An incinerator for oxidizing combustible fumes contained in amixture of such fumes and air, said incinerator comprising:

a narrow elongated burner tube having an inlet end and an outlet end;

means in said elongated tube for heating gases passing therethrough toan elevated temperature suitable for oxidizing said combustible fumes insaid mixture;

means surrounding at least a portion of said elongated tube defining apreheat zone for said mixture, said surrounding means including an inletopening for receiving said mixture, and an outlet opening fordischarging said mixture; means communicating with said burner tube andoutlet opening of said surrounding means for drawing said mixturethrough said preheat zone and for forcing the same into said burner tubeat a pressure greater than the pressure within said preheat zone;

the improvement which comprises:

said elongated burner tube comprising a plurality of elongated panels;and

means joining said panels together at the longitudinal edges thereof.

12. An incinerator according to claim 11 and further comprising surfaceextension means secured to said burner tube between said elongatedpanels to increase the heat exchange area of said burner tube.

13. An incinerator according to claim 12 wherein said surface extensionmeans comprise metal fins which extend into said 4preheat z one. I

1 An incinerator according to claim 12 wherein said surface extensionmeans comprise metal fins which extend into said burner tube.

15. An incinerator according to claim 11 wherein each of said panelscontains fastening means extending outwardly of the longitudinal edgesthereof, and said joining means extend through said fastening means toadjacent panels.

16. An incinerator according to claim 1 1 wherein said joining meanspermits escapement of gases from within said burner tube to said preheatzone to assist in heat transfer from the interior of said burner tubeinto said preheat zone.

17. In an incinerator for oxidizing combustible fumes contained in amixture of such fumes and air, said incinerator comprising:

a narrow elongated burner tube having an inlet end and an outlet end;

means in said elongated tube for heating gases passing therethrough toan elevated temperature suitable for oxidizing said combustible fumes insaid mixture; means for heat exchanging said mixture with hot gaseswithin said elongated burner tube, said heat exchange means including aninlet opening for receiving said mixture and an outlet opening fordischarging said-mixture; and

means communicating with said burner tube inlet and said outlet openingof said heat exchange means for drawing said mixture through saidpreheat zone and for forcing the same into said burner tube at apressure greater than the pressure within the preheat zone;

the improvement which comprises:

said elongated burner tube comprising a plurality of elongated panels;

means joining said panels together at the longitudinal edges thereof;and

surface extension means extending between the interior of said burnertube and said heat exchange means at said longitudinal edges of saidpanels to facilitate heat transfer between said burner tube and saidheat exchange means.

1. In an incinerator for oxidizing combustible fumes contained in amixture of such fumes and air, said incinerator comprising: a narrowelongated burner tube having an inlet end and an outlet end; means insaid elongated tube for heating gases passing therethrough to anelevated temperature suitable for oxidizing said combustible fumes insaid mixture; means surrounding at least a portion of said elongatedburner tube defining a preheat zone for said mixture, said surroundingmeans including an inlet opening for receiving said mixture and anoutlet opening for discharging said mixture; means for passing preheatedgases from said outlet opening of said surrounding means into saidburner tube; the improvement which comprises: heat exchange meansextending from within said burner tube, through said burner tube andinto said preheat zone, whereby heat is effectively transferred fromsaid burner tube to said preheat zone to preheat said mixture passingtherethrough.
 2. An incinerator according to claim 1 wherein said burnertube contains at least one turbulating means.
 3. An incineratoraccording to claim 1 wherein said burner tube comprises a plurality ofelongated panels joined together at the longitudinal edges thereof, andsaid heat exchange means are positioned between said longitudinal edgesof said elongated panels.
 4. An incinerator according to claim 3 whereinbackwardly bent flanges are formed on said longitudinal edges of saidelongated panels, and further comprising fastening means securingtogether flanges of adjacent panels with said heat exchange meanstherebetween.
 5. An incinerator according to claim 4 wherein saidfastening means extend through said flanges and through said heatexchange means, and said fastening means are spaced along the length ofsaid elongated panels, and said passing means includes a fan to drawsaid mixture through said preheat zone and to force the same into saidburner tube at a higher pressure than that of said preheat zone.
 6. Anincinerator according to claim 4 wherein said heat exchange meanscomprise elongated thin metal plates which extend into said burner tubeone-third to one-half of the radial distance between the circumferenceof said burner tube and the center thereof.
 7. An incinerator accordingto claim 4 wherein said heat exchange means comprise elongated thinmetal plates, there being a plurality of such elongated metal platesbetween each of said elongated panels, and the outer and innerlongitudinal edges of said plates are bent away from each other.
 8. Anincinerator according to claim 1 wherein said heat exchange means extenDoutwardly to said surrounding means and form spacers between said burnertube and said surrounding means.
 9. An incinerator according to claim 1wherein said surrounding means is a tubular member in concentricrelationship to said burner tube.
 10. An incinerator according to claim9 wherein said inlet opening of said surrounding means is adjacent tosaid outlet end of said burner tube, and said outlet opening of saidsurrounding means is adjacent to said inlet end of said burner tube,whereby the flow of said mixture through said preheat zone iscountercurrent to the flow of gases through said burner tube.
 11. Anincinerator for oxidizing combustible fumes contained in a mixture ofsuch fumes and air, said incinerator comprising: a narrow elongatedburner tube having an inlet end and an outlet end; means in saidelongated tube for heating gases passing therethrough to an elevatedtemperature suitable for oxidizing said combustible fumes in saidmixture; means surrounding at least a portion of said elongated tubedefining a preheat zone for said mixture, said surrounding meansincluding an inlet opening for receiving said mixture, and an outletopening for discharging said mixture; means communicating with saidburner tube and outlet opening of said surrounding means for drawingsaid mixture through said preheat zone and for forcing the same intosaid burner tube at a pressure greater than the pressure within saidpreheat zone; the improvement which comprises: said elongated burnertube comprising a plurality of elongated panels; and means joining saidpanels together at the longitudinal edges thereof.
 12. An incineratoraccording to claim 11 and further comprising surface extension meanssecured to said burner tube between said elongated panels to increasethe heat exchange area of said burner tube.
 13. An incinerator accordingto claim 12 wherein said surface extension means comprise metal finswhich extend into said preheat zone.
 14. An incinerator according toclaim 12 wherein said surface extension means comprise metal fins whichextend into said burner tube.
 15. An incinerator according to claim 11wherein each of said panels contains fastening means extending outwardlyof the longitudinal edges thereof, and said joining means extend throughsaid fastening means to adjacent panels.
 16. An incinerator according toclaim 11 wherein said joining means permits escapement of gases fromwithin said burner tube to said preheat zone to assist in heat transferfrom the interior of said burner tube into said preheat zone.
 17. In anincinerator for oxidizing combustible fumes contained in a mixture ofsuch fumes and air, said incinerator comprising: a narrow elongatedburner tube having an inlet end and an outlet end; means in saidelongated tube for heating gases passing therethrough to an elevatedtemperature suitable for oxidizing said combustible fumes in saidmixture; means for heat exchanging said mixture with hot gases withinsaid elongated burner tube, said heat exchange means including an inletopening for receiving said mixture and an outlet opening for dischargingsaid mixture; and means communicating with said burner tube inlet andsaid outlet opening of said heat exchange means for drawing said mixturethrough said preheat zone and for forcing the same into said burner tubeat a pressure greater than the pressure within the preheat zone; theimprovement which comprises: said elongated burner tube comprising aplurality of elongated panels; means joining said panels together at thelongitudinal edges thereof; and surface extension means extendingbetween the interior of said burner tube and said heat exchange means atsaid longitudinal edges of said panels to facilitate heat transferbetween said burner tube and said heat exchange means.